266 



MANUAL OF ELEMENTARY ZOOLOGY 



be grown again. The injured leg is first cast off by a 

 spasmodic contraction of some of its muscles 



and Alftotomy which causes il t0 break thr0U S h at the basi ' 



' podite, the internal cavity being here crossed by 

 a partition which leaves only a small opening, through 



Fig. 170. — Spermatozoa of a crayfish. 



A, Whole spermatozoon from above ; B, part, enlarged, in section. 

 cps. t Capsule ; pr., stiff processes. 



which the nerves and blood vessels pass. When the limb 

 is cast off this opening is quickly closed by a blood clot, 

 after which the cuticle grows across the wound. Beneath 

 the scar the new limb is formed as a sort of bud and 

 gradually takes shape. At the next moult it becomes 

 free, though it is still small, and it increases in size at each 

 moult, until a normal limb has been provided. This 



